1. Field of the Invention
The present invention relates to a power supply apparatus, an amplifier apparatus, a radio apparatus and a reproducing apparatus in which a power output is stabilized.
2. Description of the Related Art
In accordance with a low voltage of a system such as electronic products, a power supply with high accuracy used for an analog circuit is expected. In particular, a power supply apparatus free from an influence of a load as much as possible is required when electric power quality such as a voltage variation is directly linked to quality of a circuit output, such as a power amplifier at a final stage in a radio apparatus and an A-class amplifier in a reproducing apparatus.
As a characteristic showing such quality of the power supply apparatus as stated above, there is a Power Supply Rejection Ratio (PSRR). The PSRR is a ratio in which the power supply voltage variation becomes to be an input variation of an amplifier and so on. Generally, in a power supply apparatus such as a switching regulator (for example, refer to JP-A 2005-6402 (KOKAI)), the PSRR is improved by providing a large-capacity bypass capacitor and so on.
However, an addition of a component such as the capacitor may cause a large size of the power supply apparatus. Besides, it is necessary to estimate the load in advance when a capacity of the capacitor and so on are determined, and therefore, it was difficult to stabilize the power supply voltage and to improve the PSRR effectively, when the load varies.